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270 Jetting Questions

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  • 270 Jetting Questions

    I need some help with jetting on a 270. I just started racing this year and run at Lanco, I feel like I'm losing power on top end and haven't changed my Jets out since and I don't want to blow the motor, but I feel like I'm missing out on some power. I have read so many forms on jetting and reading the plug but most diagrams don't help since really lean/ rich look the same to me. I'm running a 96 power, 116 main and 245 needle jet. How low (roughly) could I go? I know some people run 80 power jet but that seems to risky for me .Are there any relative plug charts for 270? How do I use the humidity to get a good plug reading? Thanks for the help!

  • #2
    Jetting and reading plugs and other factors is something many have learned over time and quite few burned pistons. Even those who have done it for years will still push things to far and smoke a piston once in awhile.
    My advice would be to find someone at Lanco who can help you tune your engine and stay on the safe side of to lean as well as show you what things look like when the motor is tuned richer or leaner.


    • #3
      You can come talk to us at Lanco. 88D We'll tell you what we know. You are very close with what you have posted. Don't go beyond the middle rung on the 245 needle though.


      • #4
        Your best bet would be getting a mychron 4 and exhaust temp probe. then you can monitor the exhaust temp for when your motor is running good. at the same time acquire an air density reader. you should be able to use the two concurrently to determine what jets to run at what AD, and then using the plug as a guide, as well as exhaust temp, to determine how much leaner you can go based on the way the air density changes. it is definitely trial and error but you can avoid error by staying on the rich side of your trials. from my limited experience at lanco.. big jets are the way to go. maybe you're losing more with gearing or tire size than your jet size. post a photo of your plug too if you want a dissection.

        I run at a very forgiving track - bridgeport.. it is a quarter mile but it is right along the river.. air density is usually lower than most tracks.. significant humidity is usually always in the air
        I was able to be close to my desired exhaust temperature with the same main jet with feature time
        A.D. ranging from 93.7 - 97.5 -- I just adjusted my power jet at a range between 84 and 88

        so once you know where your motor runs good and takes off good, you don't have to change much to keep up with the air. you just need to keep up with the air.

        one other thing i've noticed -- with the same A.Ds... dropping the main jet by 1 should allow you to pick up 15-25 degrees in exhaust temp... dropping one to one and a half power jet size should get you 5-15 degrees in exhaust temp .. and it is almost like if you drop 1 main jet it's like dropping 2 power jets... if you want to look at it that way but it will ultimately depend on the track you're racing at and lanco and bridgeport are not equal at all... just some stuff to keep in the back of your mind when making decisions
        Last edited by alexswift; 05-02-2019, 01:43 AM.
        racing is fun.


        • #5
          Private message me. I can help